Nutrient movers Large animals help move nutrients around the landscape in much the same way as arteries carry blood around our bodies, scientists have found.

And when those large creatures become extinct, these crucial "circulatory systems" are damaged, causing long-term harm to the health of soils.

These findings come from a new analysis of events roughly 12,000 years ago, when many large animals such as giant ground sloths and car-sized armadillo-like creatures became extinct in Australia and North and South America.

Ecologist Christopher Doughty from the Environmental Change Institute at the University of Oxford and colleagues developed a new mathematical model to calculate the effect of those mass extinctions on soil nutrients.

In the journal Nature Geoscience this week they estimate the extinctions reduced the dispersal of the vital nutrient phosphorus in the Amazon by 98 per cent, with far-reaching environmental consequences that linger to this day.

There were similar, less dramatic, effects in other continents, including Australia.

New methods

Until now, there has been no way to estimate the role of so-called megafauna on nutrient transport, Doughty says.

Using a mathematical model allowed them to estimate the impact of the large animals, using data from Africa about the relationships between the size of modern-day animals and their daily movement, food consumption and lifespan.

Bigger animals carry around larger amounts of vital nutrients such as phosphorus in their bodies and dung. Also, because they move larger distances than smaller animals, they have a key role in transporting those nutrients to areas where the soil is less fertile, the researchers say.

"Our study estimates that they play a huge, important role in transporting nutrients on continental scales over thousands of years," Doughty says.

"Arteries transport nutrients broadly throughout the human body and then capillaries transport the nutrients to smaller regions. We think that large animals played this role for the planet, broadly moving nutrients…from high concentrations to low concentrations."

"Therefore, when big animals go extinct, these arteries are severed leading to more nutrient poor regions, and possibly a less healthy planet overall."

The effect of the extinction was less severe in Australia than in South America because Australia had no elephant-sized animals, which meant its animals were not as big on average.

"Since we find bigger animals are disproportionately important in this distribution process, more smaller extinctions will have a smaller effect than fewer very large animal extinctions," Doughty says.

"However, because there were so many extinctions in Australia, it still has a very large role there too."

Future risks

The scientists say their new mathematical model can also be used to predict the effect on soil fertility for thousands of years in the future if current endangered large species go extinct.

"This has a real value to people that we can now quantify and value," Doughty says. "If these animals go extinct, the health of the planet will suffer in quantifiable ways for thousands of years."

He says he's like to work with economists to put a monetary value to each large animal death based on their calculations.

"If we allow current endangered animals to go extinct, especially large ones like elephants, we will have a more nutrient poor planet in the future. The international community should recognise this and put efforts to preserve them in accordance to their value."